In recent years, network service providers have been upgrading and managing networks based on Multi Protocol Label Switching (MPLS) technology. MPLS has been deployed in most backbone networks. MPLS provides capabilities such as Quality of Service (QoS), redundancy, Operations Administration and Maintenance (OAM), and Virtual Private Network (VPN). MPLS is typically used to provision and manage data streams at individual flow levels. Each flow is known as a Label Switched Path (LSP). Existing MPLS systems typically handle data traffic at the Layer-3 (IP) level and below.
Some MPLS networks use Pseudowires to map Open System Interconnections (OSI) Layer-1 or Layer-2 traffic flows into “virtual circuits.” A Pseudowire refers to the emulation of a Layer-1 or Layer-2 native service over a network. Examples of native services include Asynchronous Transfer Mode (ATM), Frame Relay, Ethernet Virtual Local Area Network (VLAN), Time Division Multiplexing (TDM), Synchronous Optical Network (SONET), Synchronous Digital Hierarchy (SDH), etc. In the control plane, the Pseudowires are maintained and managed using a simplified version of Label Distribution Protocol (LDP), the Target LDP. Each Pseudowire is associated with an MPLS label for packet forwarding and a control word for flow management.
Since existing MPLS networks only allow Layer-1 or Layer-2 connections to be mapped to Pseudowires in a one-to-one mapping, the system typically cannot guarantee the QoS for individual applications that generate application data in Layer-3 or above. QoS behavior in the application layer is sometimes different from the behavior in Layer-1 or Layer-2. For example, packet video streams can generally tolerate out-of-sequence delivery, and packet voice traffic can sometimes tolerate packet loss but is sensitive to packet delay. Existing Layer-1 and Layer-2 systems, however, typically do not address network-level QoS for these voice and video applications.
Some proposed IP-based models have been developed to address the QoS requirement associated with applications, but some issues remain. For example, the IntServ/RSVP model identifies connections by applications based on the IP addresses of the source and destination, the protocol type, and the protocol's source and destination port number (together known as the 5-tuple). Each connection is required to comply with a number of service parameters such as bandwidth consumption and delay budget. As a result, the intermediate nodes (such as the core routers) are required to store the identity of all the connections, perform deep packet inspection, and implement extensive QoS mechanisms to satisfy the service parameters for each flow. Network service providers tend to find this model limiting because it is not very scalable as the number of users grow.
New Internet protocols, such as Session Initiation Protocol (SIP), and Real Time Streaming Protocol (RTSP), have become increasingly popular for managing application layer signaling over the Internet. One of the motivations for those protocols is that they do not require knowledge of the underlying network, thereby providing a communication mechanism for any type of user in the network. Also, control plane paths do not necessarily traverse the same data plane traffic path. As a result, the data plane does not know the service parameters associated with the control plane, which prevents the ability to provide a predictable service guarantee.
Presently SIP has been widely deployed for Voice over IP (VoIP) applications, where user traffic does not require much network resource. Service providers can therefore guarantee reasonable service guarantees by over-provisioning their networks. However, as real-time video applications are becoming popular, user traffic volume may increase to a level that the over-provisioning approach may not be sufficient to overcome persistent network congestion in all parts of the network.
Existing systems have varying levels of data plane to control plane binding. For example, in cable networks, the access devices process both the user control messages and data packets. However, this approach does not scale in large networks.
Industry standard bodies such as International Telecommunication Union (ITU) have been working on a method to communicate and facilitate user service information to data gateways. The method is known as Resource and Admission Control Functions (RACF). However, this does not work beyond a single service provider network.
The Resource ReSerVation Protocol (RSVP) is a control protocol used to reserve resources in a network for data flows. It has been proposed that, upon receiving data traffic, when an RSVP message is received at an edge node, information is exchanged between the edge node and a bandwidth broker to reserve a data path for that traffic. However, the problem with RSVP is the exchange of information is specific for RSVP-based multimedia sessions, which has no deployment in the network today.
It would be useful to have a generic technique for binding the control plane with the data plane in a network that uses SIP-based or RTSP-based protocols to manage application layer signaling. It would also be desirable for such a technique to be independent of the underlying network control protocol.